11. Twice Upon A Time
There are three elements in Capaldi's swan song episode that perfectly encapsulate what a great Doctor he is.
Firstly, the way Capaldi delivers his lines in a dexterously quicksilver way is exemplified by the snappy - in more ways than one - dialogue between his Twelfth Doctor and David Bradley's First Doctor. The former continually admonishes his first incarnation's outdated stereotypical views on men and women, and also for daring to suggest he doesn't look any younger than his future sonic sunglasses wearing self.
Secondly, Capaldi's facial expressions. You know when s**ts about to get real when his steely stare bores into anyone or when engaging those attack eyebrows. All the best actors just require a mere look to convey their thoughts and feelings. Therefore the look of utter disappointment on the Twelfth Doctor's face when he discovers there's actually no evil plan to thwart, has a mixture of irony and disappointment.
This is because we're used to seeing - and enjoying - Capaldi's Doctor positively thrive on meeting the greatest dangers head-on, but his final adventure doesn't provide any real sense of danger. Heck, even the Dalek gets naked for him.
And thirdly, Capaldi's exceptional knack of giving profound speeches. The Twelfth Doctor's brief articulation on the Christmas truce at Ypres was hauntingly poignant. Then we get to his final soliloquy.
It has all the usual bittersweet emotions you'd expect from a regeneration scene. But what makes it personal to Capaldi is his final line: "Doctor, I let you go". For Capaldi got to live his childhood dream of playing the Doctor.